vsock: switch to krun_add_vsock_port2 for listen mode support

docs/usage.md

@@ -166,10 +166,14 @@ facilitate communication between the two.
 
 Multiple instances of a `virtio-vsock` device can be specified, yet port numbers for these sockets must be unique.
 
+There are two modes - `listen` and `connect`.
+
 #### Arguments
 
 - `port`: `AF_VSOCK` port to connect to on the guest.
 - `socketURL`: Path to the UNIX socket on the host.
+- `listen`: Enable guest to host communication. (Default mode)
+- `connect`: Enable host to guest communication.
 
 #### Example
 
@@ -180,6 +184,12 @@ This adds a virtio-vsock device to a virtual machine, and will forward all guest
 --device virtio-vsock,port=1024,socketURL=/Users/user/vm-socket.sock
 ```
 
+To enable host-initiated connections to the guest:
+
+```
+--device virtio-vsock,port=1024,socketURL=/Users/user/vm-socket.sock,connect
+```
+
 ### File Sharing
 
 The `virtio-fs` option allows a guest to share a file system directory with a host. The directory can be mounted

src/virtio.rs

@@ -50,7 +50,8 @@ extern "C" {
         disk_format: u32,
         read_only: bool,
     ) -> i32;
-    fn krun_add_vsock_port(ctx_id: u32, port: u32, c_filepath: *const c_char) -> i32;
+    fn krun_add_vsock_port2(ctx_id: u32, port: u32, c_filepath: *const c_char, listen: bool)
+        -> i32;
     fn krun_add_virtiofs(ctx_id: u32, c_tag: *const c_char, c_path: *const c_char) -> i32;
     fn krun_set_console_output(ctx_id: u32, c_filepath: *const c_char) -> i32;
     fn krun_add_net_unixgram(
@@ -286,12 +287,25 @@ impl FromStr for VsockConfig {
         vsock_config.socket_url = PathBuf::from_str(socket_url.as_str())
             .context("socketURL argument not a valid path")?;
 
+        if let Some(v) = args.remove("connect") {
+            if !v.is_empty() {
+                return Err(anyhow!(format!(
+                    "unexpected value for virtio-vsock argument: connect={v}"
+                )));
+            }
+            vsock_config.action = VsockAction::from_str("connect")?
+        }
         if let Some(v) = args.remove("listen") {
             if !v.is_empty() {
                 return Err(anyhow!(format!(
                     "unexpected value for virtio-vsock argument: listen={v}"
                 )));
             }
+            if vsock_config.action == VsockAction::Connect {
+                return Err(anyhow!(
+                    "virtio-vsock argument \"listen\" and \"connect\" are mutually exclusive and cannot be used together."
+                ));
+            }
             vsock_config.action = VsockAction::from_str("listen")?
         }
 
@@ -307,7 +321,14 @@ impl KrunContextSet for VsockConfig {
     unsafe fn krun_ctx_set(&self, id: u32) -> Result<(), anyhow::Error> {
         let path_cstr = path_to_cstring(&self.socket_url)?;
 
-        if krun_add_vsock_port(id, self.port, path_cstr.as_ptr()) < 0 {
+        // libkrun's `listen` parameter means "guest expects connections from host" which is true when VsockAction::Connect.
+        if krun_add_vsock_port2(
+            id,
+            self.port,
+            path_cstr.as_ptr(),
+            self.action == VsockAction::Connect,
+        ) < 0
+        {
             return Err(anyhow!(format!(
                 "unable to add vsock port {} for path {}",
                 self.port,
@@ -322,8 +343,11 @@ impl KrunContextSet for VsockConfig {
 /// virtio-vsock action.
 #[derive(Clone, Debug, Default, PartialEq)]
 pub enum VsockAction {
+    /// Host listens for guest-initiated connections (default).
     #[default]
     Listen,
+    /// Host connects to guest; guest listens for host-initiated connections.
+    Connect,
 }
 
 impl FromStr for VsockAction {
@@ -334,6 +358,7 @@ impl FromStr for VsockAction {
 
         match &s[..] {
             "listen" => Ok(Self::Listen),
+            "connect" => Ok(Self::Connect),
             _ => Err(anyhow!("invalid vsock action")),
         }
     }